As is known, a stage lighting fixture comprises a casing housing a light source, beam filtering and profiling means, and an objective lens.
The casing extends along a longitudinal axis, is open at one end, and is closed at the opposite end, where the light source is located. In actual use, the light source, e.g. a halogen lamp, emits a beam substantially along the optical axis of the lighting fixture, which normally coincides with the longitudinal axis of the casing.
The beam filtering and profiling means are located between the light source and the objective lens to intercept the beam, are designed to produce special beam effects, and comprise, for example, beam colouring assemblies, a diaphragm, a number of gobos, and other lighting effect devices.
The diaphragm comprises a plurality of movable leaves fitted to an annular support and substantially located (overlapping) in a plane perpendicular to the optical axis. The leaves are arranged to form a substantially flat shield with a regular-polygon-shaped or circular central aperture, of which each leaf defines a side (or arc), and are movable jointly by a control and actuator to adjust the size of the central aperture. The diaphragm may be used as a dimmer or profiler to adjust the brightness or size of the lighting fixture beam respectively.
Gobos are disks, normally of stainless steel or glass, shaped or patterned to produce given lighting effects when they intercept the beam.
The objective lens is located at the open end of the casing, is substantially perpendicular to the optical axis, and is movable to adjust its focus position with respect to the beam filtering and profiling means.
Known lighting fixtures provide for a fairly wide, but somewhat limited, range of lighting effects. For example, the devices normally featured in lighting fixtures are unsuitable for projecting variable-sized shapes other than convex polygons.